白云石化
白云石
地质学
方解石
镁
矿物学
化学
古生物学
有机化学
相
构造盆地
作者
Chia Pei Teoh,Juan Carlos Laya,Katharine Rose,Stephen E. Kaczmarek
出处
期刊:Journal of Sedimentary Research
[Society for Sedimentary Geology]
日期:2022-02-22
卷期号:92 (2): 134-143
被引量:5
摘要
ABSTRACT Selective dolomitization of HMC allochems in Neogene carbonates is a common phenomenon. It has been proposed that the higher magnesium concentrations [Mg] in these allochems promotes dolomitization. To directly investigate the effects of [Mg] (reported as mol% MgCO3) in biogenic HMC on dolomitization, high-temperature (200 °C) dolomitization experiments were conducted. Dolomite reaction rate, stoichiometry, and microstructures were tracked during dolomitization for a variety of biogenic HMC reactants, including Goniolithon, Lithothamnion, Lithophyllum, Corallina officinalis, Heterocentrotus mamillatus, and Mellita quinquiesperforata. Solids were characterized using standard powdered X-ray diffraction (XRD) and scanning electron microscopy (SEM). In general, biogenic HMC reactants are progressively replaced by protodolomite products between 2 and 46 hours. In the experiment using Corallina officinalis, no products were detected by XRD after 46 hours. Initial protodolomite products are subsequently replaced by ordered dolomite as the reactions proceed. Dolomitization rate and protodolomite stoichiometry do not correlate with [Mg] of the biogenic HMC reactants. Dolomitized HMC skeletons reliably retain the original microstructure of the HMC reactants, consistent with the microcrystalline mimetic textures observed in nature. These findings collectively suggest that under the conditions investigated, dolomitization is less affected by the concentration of magnesium in the HMC reactants relative to other known factors, such as temperature, reactant mineralogy, organic content, skeletal texture, and fluid chemistry. These results imply that the observed correlation between coralline red algae abundance and global dolomitization events in the Neogene is not driven by the elevated magnesium concentration of the HMC reactants.
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